1. Field of the Invention
The present invention relates to a reversible thermosensitive recording material which is capable of forming images therein and erasing the same therefrom by utilizing the performance that a reversible thermosensitive recording layer of the recording material reversibly assumes a transparent state and a white opaque state depending upon the temperature thereof.
2. Discussion of the Background
Reversible thermosensitive recording materials are conventionally known, as disclosed in Japanese Laid-Open Patent Applications 54-119377 and 55-154198. These conventional reversible thermosensitive recording materials have the shortcoming that a temperature range where the reversible thermosensitive recording material assumes a transparent state is as narrow as 2.degree. to 4.degree. C. Because of such a narrow temperature range, temperature control is difficult in forming images in the recording material by utilizing the reversible change between the transparent state and the white opaque state of the reversible thermosensitive recording material.
To eliminate the above-mentioned shortcoming, a particular higher fatty acid ester is used as a eutectic agent in the reversible thermosensitive recording material, as disclosed in Japanese Laid-Open Applications 63-39378 and 63-130380. In the above-mentioned applications, however, the temperature range is increased toward the low temperature side. There remains a problem of the obtained images disappearing at a temperature of 50.degree. to 60.degree. C.
In Japanese Laid-Open Patent Application 3-2089, the inventors of the present invention have proposed to use an aliphatic dicarboxylic acid having a high melting point in the reversible thermosensitive recording layer in order to increase the temperature range where the reversible thermosensitive recording material can assume a transparent state toward the high temperature side. As a result, the preservability of the images can be ensured at temperatures of 50.degree. to 60.degree. C.
In line with diversified usage and with the development of the market for reversible thermosensitive recording materials, there is an increasing demand for the capability of preserving the image at temperatures as high as 70.degree. to 80.degree. C. More specifically, the above-mentioned demand is directed to the case where the reversible thermosensitive recording material is used or stored, for example, exposed to direct sunlight, or left in a closed car in the summer. Accordingly, it is necessary to further increase the temperature range where the reversible thermosensitive recording material assumes a transparent state toward the high temperature side.